Wiping applicators are known in the art of applying herbicide to weeds. The applicators depend on utilization of the height differential that in many cases exists, for a period of time, between the targetted weeds and the crop plants. The concept inherent in these devices is to bring the absorbent material, suspended from a height-adjustable frame and soaked with herbicide, into contact only with the weeds.
Application of herbicide in this manner is characterized by minimal wastage of herbicide and little damage to the crop.
U.S. Patents which are of interest in connection with such applicators are: Nos. 4,208,835 (Roll et al); 4,223,478 (McHugh); 4,253,272 (Bertness); 4,274,589 (Jones); 4,285,160 (Barton); 4,302,904 (Mead); 4,320,595 (McClure); 4,377,920 (Bowman); and 4,446,650 (Davis).
In the first attempt to provide an applicator, applicant used a length of sewer pipe, which was closed at its ends to form a chamber containing a reservoir of liquid herbicide. A long, rectangular strip of carpet material was provided, having its upper longitudinal edge extending into the reservoir through a slot in the top of the pipe. The strip hung down like a curtain from the pipe. This embodiment provided a good "profile", in that the lower edge of the carpet strip was generally parallel to the ground. However, considerable difficulty was encountered in locating a material which would "wick" properly and bring the herbicide to the lower edge of the strip at a desirable rate. Also, when the assembly was moving along a hillside, the liquid would accumulate at the lower end of the pipe and would flood the carpet strip at that end, while the strip at the upper end would be starved for liquid. In addition, the assembly was only capable of supplying the herbicide to the strip lower edge at one rate, so there was no way of varying the amount of herbicide wiped on. Thus variations in weed density could not be accommodated or dealt with, except by varying the speed at which the applicator was moved along.
From the background work with this assembly, it became clear that an applicator should be characterized by the following desirable features:
good wicking capability; PA1 the capability to vary the rate of herbicide supply to the surface contacting the weeds; PA1 the capability to "store" herbicide at the contacting surface, to cope with temporary changes in demand, as when contacting a dense stand of weeds of limited extent; PA1 the provision of a wiping element which could not be easily penetrated by brush and torn away and which presented a level profile; PA1 the capability to uniformly supply herbicide along the length of the wiping element, When moving alqng an incline; PA1 and rugged and simple construction.